1. Field of the Invention
The present invention relates to a starter of an internal combustion engine of an automobile or the like and, in particular, to a structure for mounting a washer for regulating the movable distance of an armature in the direction of thrust.
2. Description of the Related Art
As a publicly known technology relating to a starter, a technology is disclosed in Japanese Unexamined Patent Publication No. 7-310631. In this starter, the shaft of a revolving armature supported by a bracket via a bearing has a groove made in a circumferential direction (hereinafter sometimes referred to as a circumferential groove) near its one end and a holder plate for holding a brush is fixed to the inside of the end surface of the bracket with screws and the outer peripheral portion of a washer is sandwiched by the bracket and the holder plate and the inner peripheral portion of the washer is fitted in the circumferential groove to regulate the movable distance of the armature in the direction of thrust (in the axial direction). The movable distance is a gap in the axial direction between the washer and the circumferential groove and is set within a given range (for example, 0.2 mm or less) based on the relationship between the width of the circumferential groove and the thickness of the washer.
The above-mentioned publicly known technology limits the movable distance of the armature in the direction of thrust within a given range and does not disclose adequate findings on the relationship between the rigidity of the washer holding the armature and vibration noises generated when the washer receives a thrust load.
In the case where a great deal of thought is not given to the rigidity of the washer holding the armature, large vibrations in the direction of thrust are produced during the rotation of the armature to vibrate the bracket, which might in turn make the bracket itself produce resonance. Therefore, it is required to provide a technology to reduce these vibrations and noises.
It is the object of the present invention to provide a starter capable of reducing noises when the starter is put in motion with a simple modification to its structure without increasing the number of parts.
The present inventor has well studied the publicly known technology and has found that the positions of screws for fixing a holder plate pressing a washer for regulating the movement of an armature in the direction of thrust greatly relates to the vibrations and noises generated when the starter is put in motion and hence constitutes the present invention basically in such a way as is described in the following, so as to accomplish the above-mentioned object.
(1) According to the first invention, there is provided a starter comprising an armature provided with a shaft having a groove made in a circumferential direction near its one end, a bracket provided with a bearing rotatably supporting the one end of the shaft, a holder plate for holding the brush of a motor, screws for fixing the holder plate to the inside of the end surface of the bracket, and a washer having an inner peripheral portion fitted in the groove made in the circumferential direction of the shaft and an outer peripheral portion sandwiched between the bracket and the holder plate, the washer limiting the movement of the armature in the axial direction, wherein, letting the pitch of the screws=L when the screws for fixing the holder plate to the bracket are spaced 180 degrees apart, the outer diameter of the washer=D1, the outer diameter of the screw=D2, and the thickness of the holder plate=t, they satisfy the following Formula 5,
D1+D2 less than Lxe2x89xa6D1+D2+5txe2x80x83xe2x80x83(Formula 5)
(2) According to the second invention, there is provided a starter in which the condition of the pitch L is relaxed as compared with the first invention, wherein, letting the pitch of the screws=L when the screws for fixing the holder plate to the bracket are spaced 180 degrees apart, as is the case with the first invention, the outer diameter of the washer=D1, the outer diameter of the screw=D2, and the thickness of the holder plate=t, they satisfy the following Formula 6,
D1+D2 less than Lxe2x89xa6D1+D2+10txe2x80x83xe2x80x83(Formula 6)
In the first and second inventions, the present invention is defined by the pitch L of the screws for fixing the holder plate which are spaced 180 degrees apart. However, the number of the screws is not limited to two but may be more than two and the spacing of the screws may be different from the 180 degrees. In this case, the following invention will be proposed so as to accomplish the above-mentioned object.
(3) According to the third invention, there is provided a starter in which, letting the distance between the center of the shaft of the armature and the center of the screws=R, the outer diameter of the washer=D1, the outer diameter of the screw=D2, and the thickness of the holder plate=t, they satisfy the following Formula 7,
(D1+D2)/2 less than Rxe2x89xa6(D1+D2+5t)/2xe2x80x83xe2x80x83(Formula 7)
The above-mentioned Formula 7 (Formula 3) is equivalent to the Formula 5 (Formula 1).
(4) According to the fourth invention, there is provided a starter in which the condition of the third invention is relaxed, that is, letting the distance between the center of the shaft of the armature and the center of the screws=R, the outer diameter of the washer=D1, the outer diameter of the screw=D2, and the thickness of the holder plate=t, they satisfy the following Formula 8,
(D1+D2)/2 less than Rxe2x89xa6(D1+D2)/2+5txe2x80x83xe2x80x83(Formula 8)
In this connection, the above-mentioned Formula 8 (Formula 4) is equivalent to the Formula 6 (Formula 2).
The detailed description of the present invention, in particular, the reason of the Formulae will be described in detail in the following preferred embodiment.